The present invention relates to drum scanners and plotters generally, and more specifically, to a method and apparatus for position referencing a rotating drum in a scanner/plotter.
Drum scanners and photoplotters are well known in the image processing art. In order to accurately scan or photoplot in a drum scanner or plotter, the position of the drum must be accurately referenced to the optical axis of the scanner/plotter. The prior art has accomplished the requisite accurate position referencing of the drum by utilizing tight mechanical tolerances for the drum, the drum drive system and the scanner/plotter head. The use of tight mechanical tolerances is a satisfactory solution to the drum position referencing problem when the drum constitutes a substantially permanent part of the scanner/plotter. However, if the drum is frequently removed from the scanner for attachment of copy of for loading or unloading film, the use of tight mechanical tolerances imposes an undesirable cost burden on the scanner/plotter system.
It is accordingly a general object of the present invention to provide an improved method and apparatus for position referencing a rotating drum in a scanner/plotter.
It is a specific object of the invention to provide a method and apparatus for position referencing a rotating drum without requiring tight mechanical tolerances between the drum and the scanner/plotter.
It is another object of the invention to provide a position referencing system for a rotating drum which does not require the drum to be initially aligned with a reference element in the scanner/plotter.
It is a feature of the present invention that the apparatus can be implemented with readily available components.
It is another feature of the invention that the removable drum can be relatively inexpensively fabricated without requiring tight mechanical tolerances.